This application is related to Xerox docket No. 0740 (IP/A00102).
Not Applicable
1. Field of the Invention
The present invention relates to gain control, and more particularly, to such control when used with ESVs (electrostatic voltmeters) in xerographic copying machines.
2. Description of the Related Art Including Information Disclosed Under 37 CFR 1.97 and 1.98
In xerographic copying machines it is desired to measure the potential on a photoreceptor to achieve better copy quality. This is done using an ESV. However, the standard xe2x80x9cfeedbackxe2x80x9d ESV is a second order feedback system. The xe2x80x9cspeed of responsexe2x80x9d of the ESV is dependent on the open loop gain of the system, which is dependent on both the spacing between a sense probe or head and the mechanical modulation (change in the spacing). In practice, there is an electronic gain control that is adjusted in the factory setup procedure to give the desired output response at the calibration spacing and the assumption is made that the amount of modulation stays constant. If the system gain is xe2x80x9chighxe2x80x9d, the output will overshoot the final value. If it is xe2x80x9clowxe2x80x9d, it will be slow or underdamped. If it is xe2x80x9coptimizedxe2x80x9d, it is xe2x80x9ccriticallyxe2x80x9d damped, i.e., it is going as fast as possible without overshooting.
In the past, it has been assumed that the amount of gain remains constant. In fact, it is dependent on a stable modulating structure, such as the standard tuning fork and the newer ASIC (application specific integrated circuit) ESV xe2x80x9cvibrating beam. Such structures can gave gains that vary with time, temperature, etc. Also, circuits in such structures can be floating at the high photoreceptor voltage, thereby making gain adjustment difficult.
It is therefore desirable to have an adjustable gain, even when the ESV is floating at a high voltage, in order to maintain optimum gain, and thus response speed.